The goal of this project is to study the molecular basis of T lymphocyte differentiation. A number of cell surface glycoroteins have been identified which characterize specific stages of human T cell maturation and which may be involved in the function of these cells. We plan to use monoclonal antibodies produced by us and others to further study these important glycoproteins. The antibodies will be used to study the biosynthesis and intracellular processing of their respective antigens in T cells at various stages of differentiation. In addition, the expressin of T cell antigens will be studied in leukemia cells and in leukemia cell lines. The antibodies will be used to select expression variants of these leukemia cell lines. Messenger RNA coding for specific antigens will be isolated and cDNA will be cloned in bacteria. Genes that code for these antigens will be identified and structurally characterized. These genes will be used as probes to study the regulation of their expression in normal differentiation and in leukemia. We will test the hypothesis that leukemia cells represent specific stages of normal T cell differentiation.